QHY168c Digital Gain Question

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glauria
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Joined: Wed May 30, 2018 7:15 pm

QHY168c Digital Gain Question

#1

Post by glauria »

I have a QHY 168c, and I'm trying to determine which value I should use for the digital gain. In reading some of the forums, Dr. Glover states that it should not be used while imaging and is only meant as a tool to find stars. By not using it, I would assume that its value should be set to "1", but when I use this value, my images a way too dark. From trial and error, I am using a value of 10. Is this O.K.?

Clear skies,
-Gene
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Re: QHY168c Digital Gain Question

#2

Post by admin »

Hi Gene,

the best way to find the 'neutral' setting for digital gain controls (also works for colour balance controls on some cameras that have digital colour balance adjustments) is to watch the histogram as you adjust the setting.

Do this in 8 bit mode, while viewing a daylight image with a wide range of brightness.

If a digital adjustment is boosting or reducing the brightness, you usually see gaps or peaks in the histogram that are regularly spaced - as shown below in the red channel
Screenshot 2024-03-02 142414.jpg
Screenshot 2024-03-02 142414.jpg (28.06 KiB) Viewed 191 times
Compare the red channel with peaks every 2 to 3 levels with the blue channel that is smooth - in this case I had set the red white balance of a PlayerOne camera to boost the red channel.

If a digital adjustment is reducing the brightness, you may see the histogram not reaching all the way across to the 100% point even if the image contains saturated areas. If you observe this then the procedure to find the correct value is easy - turn up until the histogram just reaches 100%.

From experience, it might well be that the 'neutral' value is a power of two for QHY cameras - 16, 32, 64, etc.

cheers,

Robin
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